The invention relates to a hydraulic camshaft adjuster for a camshaft of an internal combustion engine with a hydraulic operating mechanism for adjusting the angular position of the camshaft relative to the crankshaft.
To lower fuel consumption and untreated emissions and to increase power and torque, many gasoline engines are equipped with camshaft adjusters. These vary the phase position of the camshaft in relation to the crankshaft. Hydraulic vane-cell adjusters are mostly used at the present time, which have an outer body connected for rotation with a driving wheel and an inner body rotatably disposed in the outer body and connected for rotation with the camshaft. The outer body has at least one hydraulic chamber and the inner body has at least one pivot vane which divides the hydraulic chamber into two working chambers. Adjustment is carried out by means of a controlled supply of oil from the engine circuit into the respective working chamber via a control valve. The control valve is operated by means of an electromagnetic device. Since, when the internal combustion engine is operating, the pivot vane of the inner body is subjected to the changing moments of the camshaft, it is necessary at operating times when there is still no oil pressure present at the camshaft adjuster, such as, for example, during starting of the internal combustion engine, or the oil pressure level is too low for the adjusting operation, to provide a locked basic and emergency operative position by means of a corresponding mechanism. Consequently, at these operating points, undefined control time changes due to the oscillation of the pivoting vane with respect to the housing must be prevented and noises resulting therefrom should be minimized.
DE 102 53 496 A1 discloses a generic camshaft adjuster for adjusting the rotary angle of the camshaft with respect to a crankshaft of an internal combustion engine. The camshaft adjuster has an outer body connected fixedly in terms of rotation to a driving wheel and an inner body connected fixedly in terms of rotation to the camshaft, the outer body having at least one hydraulic chamber and the inner body at least one pivoting vane which divides the hydraulic chamber into two working chambers. The pivoting vane is pivotable hydraulically between a late stop and an early stop by means of a controlled oil pressure and, in its middle position between the two stops, has the basic position which can be locked by means of two spring-loaded and hydraulically releasable locking bolts which for locking engage in each case into a locking groove/bore. The locking bolts prevent an unwanted movement of the camshaft adjuster when there is no oil pressure present.
In hydraulically operated camshaft adjusters which are not to maintain their locked basic position of the mechanical stops for limiting the adjustment range, but, instead, in a defined intermediate position within this range, there is the problem that, when the internal combustion engine is in controlled operation, the pivoting vane or the hub of the inner body must move over the locking base position, without the movement of the pivoting vane being impeded by an undesirable engagement of the locking bolt which may be triggered, in particular, by fluctuations of the oil pressure from the oil supply or a brief undershooting of pressure due to oscillations of the inner body with respect to the outer body.
It is the object of the present invention, therefore, to provide a hydraulic camshaft adjuster in such a way that a reliable release of the camshaft adjuster lock and a reliable disengagement state can be achieved.